1. Field of the Invention
This invention relates to a sliding type magnetic head for magneto-optical recording which contacts with and slides on a magneto-optical record medium to effect magneto-optical recording of the record medium.
2. Description of the Related Art
Various writable optical disks for which writing, erasure and reading out can be performed using a beam of light are already known, and one of the writable optical disks is a magneto-optical disk.
General construction of a magneto-optical disk is shown in FIG. 87. Referring to FIG. 87, the magneto-optical disk 1 shown includes a transparent substrate 2, a magneto-optical recording layer 3 formed from a vertical magnetization film and provided on the transparent substrate 2, a reflection film 4 formed from, for example, a thin aluminum film and provided on the magneto-optical recording layer 3, and a protective film 5 made of, for example, a resin of the ultraviolet radiation setting type and formed on the reflection film 4.
Magnetic field modulation, light modulation and so forth are known as recording methods for a magneto-optical disk.
The magnetic field modulation allows so-called overwriting wherein a new signal is written over an old signal. In magneto-optical recording according to the magnetic field modulation, as shown in FIG. 86, an optical pickup for irradiating laser light 6 and magnetic field generating means which moves in synchronism with a laser spot, that is, a magnetic head 4, are disposed on the opposite sides of a magneto-optical disk 1 having a magneto-optical recording layer formed from a vertical magnetization film. In particular, the former is disposed adjacent the substrate 2 of the magneto-optical disk 1 while the latter is disposed adjacent the protective film 5 of the magneto-optical disk 1. Thus, the direction of the magnetic field generated by the magnetic head 7 is varied by varying the direction of an electric current to flow through the magnetic head 7.
The magneto-optical disk 1 is rotated at a predetermined speed around an axis at the center thereof.
As a magnetic field corresponding to a recording signal is formed around a laser spot 6a, a portion 1A of the disk 1 to be re-written is heated to a temperature higher than its Curie temperature at the laser spot 6a so that it is demagnetized. Then, the portion 1A of the disk 1 moves away from the laser spot 6a, and consequently, the temperature thereof drops to a level lower than the Curie temperature. In this condition, the portion 1A of the disk 1 is magnetized in the direction of the magnetic field generated by the magnetic head 7 to effect magnetic recording thereof.
A conventional magneto-optical disk is a non-contacting medium, and accordingly, the magnetic head 7 is disposed in a spaced relationship by a necessary and sufficient distance d0 from the magneto-optical disk 1.
Since a conventional magneto-optical disk is recorded in a non-contacting condition as described just above, an electromagnetic servo mechanism is provided for the magnetic head 7 for magneto-optical recording so that the magnetic head 7 may follow up deflection of the disk 1 in a lateral direction to and from its plane which takes place when the disk 1 rotates while the magnetic head 3 remains spaced away from the disk 1 and which is caused by an inclination, an uneven thickness or the like of the disk 1. Accordingly, a recording and reproducing machine which records and reproduces a magneto-optical disk in a non-contacting condition is limited in reduction of the power dissipation, reduction in size (particularly in thickness) and so forth.
The inventor of the present invention has proposed a sliding type magnetic head which contacts with and slides on a magneto-optical disk upon recording or reproduction. The sliding type magnetic head is shown in FIG. 88. Referring to FIG. 88, the sliding type magnetic head 11 includes a head element 14 wherein a coil 13 is wound around a center magnetic pole core 12A of a ferrite core member 12, and a sliding member 15 provided along a peripheral portion of a lower face of the head element 14 and having a coefficient of friction lower than that of the ferrite core member 12.
In the sliding type magnetic head 11, the sliding member 15 contacts with and slides on the disk 1 while the center magnetic pole core 12A is opposed to the disk 1 in a spaced relationship by a small distance d1 and does not contact directly with the disk 1. Accordingly, the center magnetic pole core 12A will not damage the protective film 5 of the disk 1 at all.
Further, since the magnetic head 11 is of the contacting type wherein it contacts with and slides on the magneto-optical disk 1, it can be supported by way of such a simple structure that it is mounted on a head arm by way of a resilient supporting member of itself, and a conventionally employed electrode servo mechanism which occupies a large volume can be eliminated. Accordingly, the sliding type magnetic head 11 is advantageous in reduction of the power dissipation of a recording and/or reproducing apparatus and in miniaturization of the equipment. Further, since the magnetic head 11 comes closer to the disk 1 than a magnetic head of the non-contacting type, the magnetic field acting upon the disk 1 is higher in intensity, and consequently, the recording power can be reduced.
By the way, with the magnetic head 11 described above, there is the possibility that, when it is acted upon by an impact from the outside, it may be spaced away from the disk 1.
The supporting mechanism for the magnetic head 11 described above is shown as a model in FIG. 90. Referring to FIG. 90, the magnetic head 11 is supported on a head arm 18 by way of a spring member 17 so that it is normally held in resilient contact with a surface 1a of the disk 1 under the resilient force of the spring member 17.
Now, if it is assumed that an acceleration a is applied to the head arm 18 and the disk 11 from an external force, then when the acceleration a acts in the downward direction, the magnetic head 11 will be spaced away from the disk 1 since it tries to keep its present position due to the magnetism. In particular, in the configuration shown in FIG. 90, a force F which is equal to the product of the acceleration a and the mass of the magnetic head 11 is generated in the upward direction. Accordingly, the magnetic head 11 and the disk 1 will be spaced away from each other if a spring force greater than the force F but acting in the opposite direction does not act upon the magnetic head 11.
Accordingly, for an external impact, a method is taken wherein a load force which increases in proportion to a forecast acceleration a is applied to the sliding member of the magnetic head. Consequently, the sliding resistance is increased, and as a result, there is the possibility that the damage to the disk 1 may be increased and the load to a spindle motor for driving the disk 1 to rotate may be increased. Further, abrasion of the sliding member 15 may not be ignored any more.
Furthermore, where there is some irregular variation in profile such as a bump 16 on the surface 1a of the disk 1, when the sliding member 15 of the magnetic head 11 passes the bump 16, the magnetic head 11 will be caused to jump by an amount of the height h1 of the bump 16 and be spaced away from the surface la of the disk 1. Consequently, the recording capacity is dropped. Accordingly, in order to maintain the recording capacity of the magnetic head 11, the magnetic head 11 must have a high output.
Further, since the apparent weight of the sliding type magnetic head 11 then is, according to the conventional supporting mechanism, the mass of the magnetic head 11 itself, the impact upon the disk 1 is high. If the impact is excessively high, then the disk 1 will slide on the magnetic head 11, resulting in a defocused condition of the optical system.
In order to reduce the impact, it seems an effective measure to reduce the mass of the magnetic head 11 and accordingly reduce the size and weight of the head 11 itself. However, if the magnetic head 11 is made small, then the head output is reduced contrary to the object of using a head of a high output described above.